We are reminded that testing a 24x7 infrastructure is a Very Hard Problem.
Door locks that depend on internet-access, large enterprise products that depend on unidentified network resources. If you can't disable part of your environment to see what else breaks, you really have no idea.
Obviously, door locks shouldn't depend on internet access and if you decided they should depend on a working LAN, you better make sure it's fully in your control.
I've worked in environments where the NetApp systems and the DNS-systems were mutually dependant, and this was only discovered while bringing an entire datacenter back online after a power outage.
I've worked in environments where supposedly stand-alone, hour long compile processes depended on network resources. This was only discovered when the network failed at a critical time of software release.
Other engineering disciplines (water, power, etc) have had this problem for centuries.
At least in IT environments, you have the option to automatically re-create your environment somewhere isolated and see what happens when parts of your re-created test setup dies.
Design for offline functionality
This is actually my biggest concern with 'the cloud'.
Everything becomes dependant on reliable, high-speed networks. I personally try to work around having to depend on reliable networks: Instead of a web-based CMS that requires network access to edit content in-place, I have a static website that I edit offline and upload when I'm on a fast network.
I sync my IMAP account to local disk, so I don't have to wait for network latency or service availability.
Most of my work these days is stored in git, so I can work fully offline while making it easy to backup and share my work whenever I'm on a fast network.
Google Reader fetches content from around the internet and stores all my feeds until my offline client connects to Google Reader and downloads a full copy. I can get to my desired content regardless of how broken these sites are, because only the route between my computer and Google needs to function.
I know these are very simple examples (and some, like Google Reader, have privacy implications) but anytime you can design a system that allows for full offline mode, while making the best of a network when it's available, I think that's a golden design to shoot for.
Just as a suggestion: Perhaps door locks should be able to cache some sort of credentials for X hours or days to prevent network problems from rendering an entire hotel inoperable.